Illumination system using a plurality of light sources

ABSTRACT

An illumination system includes a plurality of radiation generating sources, such as LED dies. A corresponding plurality of optical waveguides is also provided, with each waveguide having a first and a second end, with each first end being in optical communication with the corresponding LED die. An array of corresponding passive optical elements is interposed between the plurality of LED dies and the corresponding first ends of the plurality of optical waveguides. The illumination system provides for substantially high light coupling efficiency and an incoherent light output that can appear to the human observer as arising from a single point of light. In addition, the light can be output remotely at one or more locations and in one or more directions.

RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 60/430,230, filed on Dec. 2, 2002, the entirety of whichis incorporated by reference herein. The present application is alsorelated to co-owned and concurrently filed U.S. Patent applicationsentitled “Solid State Light Device” Ser. No. 10/726,225; “ReflectiveLight Coupler” Ser. No. 10/726,244; “Multiple LED Source and Method forAssembling Same” Ser. No. 10/726,248; and “Illumination Assembly” Ser.No. 10/727,220, each of which are incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lighting or illumination assembly andsystem. More particularly, the present invention relates to a highcoupling efficiency illumination system including a plurality of lightsources.

2. Background Art

Illumination systems are used in a variety of applications. Home,medical, dental, and industrial applications often require light to bemade available. Similarly, aircraft, marine, and automotive applicationsrequire high-intensity illumination beams.

Traditional lighting systems have used electrically powered filament orarc lamps, which sometimes include focusing lenses and/or reflectivesurfaces to direct the produced illumination into a beam. However, incertain applications, such as in swimming pool lighting, the final lightoutput may be required to be placed in environments in which electricalcontacts are undesirable. In other applications, such as automobileheadlights, there exists a desire to move the light source from exposed,damage-prone positions to more secure locations. Additionally, in yetother applications, limitations in physical space, accessibility, ordesign considerations may require that the light source be placed in alocation different from where the final illumination is required.

In response to some of these needs, illumination systems have beendeveloped using optical waveguides to guide the light from a lightsource to a desired illumination point. One current approach is to useeither a bright single light source or a cluster of light sourcesgrouped closely together to form a single illumination source. The lightemitted by such a source is directed with the aide of focusing opticsinto a single optical waveguide, such as a large core plastic opticalfiber, that transmits the light to a location that is remote from thesource/sources. In yet another approach, the single fiber may bereplaced by a bundle of individual optical fibers.

The present methods are very inefficient with approximately 70% loss ofthe light generated in some cases. In multiple fiber systems, theselosses may be due to the dark interstitial spaces between fibers in abundle and the efficiencies of directing the light into the fiberbundle. In single fiber systems, a single fiber having a large enoughdiameter to capture the amount of light needed for bright lightingapplications becomes too thick and loses the flexibility to be routedand bent in small radii.

Some light generating systems have used lasers as sources, to takeadvantage of their coherent light output and/or low divergence angle.However, laser sources typically produce a single wavelength outputcolor whereas an illumination system typically requires a more broadbandwhite light source. For example, U.S. Pat. No. 5,299,222 discusses theuse of single wavelength high-power laser diodes to couple energy into awavelength sensitive gain medium, as opposed to use as an illuminationsource. The use of the specified laser diodes, with their asymmetricalbeam shape, requires the extensive use of optical beam shaping elementsin order to achieve more efficient coupling into the optical fibers.Also, some laser diodes are expensive to utilize since they requirestringent temperature control (e.g., the need for using thermoelectriccoolers, and the like) due to the heat they generate in operation. Inaddition, a concentrated array of packaged LEDs can lead to problems inthe area of thermal management.

The need remains for a lighting system that can deliver high-intensityillumination using a light source.

SUMMARY OF THE INVENTION

The present invention relates to a lighting or illumination assembly.More particularly, the present invention relates to a high couplingefficiency illumination system including a plurality of light sourcesthat can be arranged remotely from the illumination output.

A lighting or illumination system, referred to herein as an illuminationdevice, in accordance with the present invention comprises a pluralityof LED dies, a corresponding plurality of optical waveguides, eachhaving first and second ends, each first end being in opticalcommunication with the corresponding LED die, and an array ofcorresponding optical elements interposed between the plurality of LEDdies and the corresponding first ends of the plurality of opticalwaveguides.

In exemplary embodiments, the light sources are individual LED dies orchips, or laser diodes. The waveguides may include optical fibers, suchas polymer clad silica fibers. The first ends of the plurality ofoptical waveguides receive the light emitted from the light sources. Thesecond ends of the plurality of optical waveguides may be bundled orarrayed to form a single light illumination source when illuminated.

The optical elements may include passive optical elements, such as anarray of input light-directing or concentrating elements, wherein eachwaveguide first end is in optical communication with at least one lightdirecting/concentrating element and wherein the array of lightdirecting/concentrating elements is in optical communication with andinterposed between the LED dies and the first ends of the plurality ofoptical waveguides.

In an exemplary embodiment, the array of optical elements comprises anarray of reflectors. These reflectors can be shaped to preserve ormaintain the small étendue of the LED die light source and tosubstantially match this étendue to the étendue (which is proportionalto the product of the core area and acceptance angle) of the lightreceiving fiber. The array of reflectors can be formed in a substrate,such as a multilayer optical film (MOF) or a metallized substrate orsheeting.

The illumination device may further comprise at least one outputlight-directing element, such as a collimating, collecting, or beamshaping element that directs light from the second ends to form a singleillumination source. The output light-directing elements may comprise anarray of light-directing elements, wherein each second end is in opticalcommunication with at least one light-directing element.

Alternatively, the plurality of waveguides may comprise a plurality ofoptical fibers and the output light-directing elements comprise fiberlenses on each second end of the plurality of optical fibers. Similarly,the first end of the optical fibers may further comprise a fiber lens.

In another embodiment, the illumination device further includes a secondplurality of LED dies and a second plurality of optical waveguides, eachhaving first and second ends, each first end of the second plurality ofoptical waveguides being in optical communication with one of the secondplurality of LED dies. In an exemplary embodiment, the second ends ofthe second plurality of optical waveguides are bundled with the secondends of the first plurality of optical waveguides to form a single lightillumination source when illuminated. Alternatively, the second ends ofthe first plurality of optical waveguides are formed in a first bundleand the second ends of the second plurality of optical waveguides areformed in a second bundle to form separate illuminating outputs that canbe directed in the same or in different directions.

These first and second light sources may have different emissionspectra. In one particular embodiment, the emission spectrum of thefirst plurality of LED dies is essentially white light, while the secondplurality of LED dies includes an infrared source. In anotherembodiment, the two (or more) pluralities of LED dies include differentcolors to allow for the blending non-white colors. The first and secondpluralities of LED dies may be illuminated individually or collectivelyto vary the intensity of the illumination source.

Additionally, the system may comprise at least one output opticalelement that is optically coupled to direct output light from the secondends of the first plurality of optical waveguides along a first path anda second output optical element that is optically coupled to directoutput light from the second ends of the second plurality of opticalwaveguides along a second path.

Such embodiments may be applied as a headlight illumination system foran automobile or other vehicle or platform. In one exemplary embodiment,the intensity of the headlight beam can be controlled by illuminating aparticular number of LED chips of the array of light sources. Forexample, a first plurality of LED dies may be illuminated for a low beamand the first and/or a second plurality of LED dies may be illuminatedfor a high beam.

In another exemplary embodiment, the illumination system can furthercomprise an infrared sensor for, e.g., collision detection,illumination, and/or telemetry applications.

The above summary of the present invention is not intended to describeeach illustrated embodiment or every implementation of the presentinvention. The figures and the detailed description that follow moreparticularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illumination system in accordancewith an embodiment of the present invention.

FIG. 2 is a simplified cross-sectional side view of a light source usedin an illumination system in accordance with an embodiment of thepresent invention.

FIG. 3 is a detail view of a portion of the light source and reflectorsurface in accordance with an embodiment of the present invention.

FIG. 4 is a graph representing the curve shape plot of reflector pointsassuming an 80 degree maximum emission angle and a 30 micrometerseparation between the LED die and the reflector.

FIG. 5 is a cross-sectional side view of an embodiment of a lightconcentrating element in accordance with an embodiment of the presentinvention.

FIG. 6 a shows an example single light receiving fiber and FIG. 6 bshows an example bundle of light receiving fibers.

FIG. 7 is a partially exploded view of an array of interconnected LEDdies and an array of optical concentrating elements used in anillumination system in accordance with an embodiment of the presentinvention.

FIGS. 8–11 are cross-sectional end views of alternative embodiments ofan optical connector used in an illumination system in accordance withthe present invention.

FIG. 12 is a simplified illustration of an assembling setup for thesimultaneous manufacture and termination of cable assemblies.

FIG. 13 is an exploded perspective view of a vehicle illumination systemin accordance with an embodiment of the present invention.

FIG. 14 is an example construction of a multilayer, high density solidstate light source.

FIGS. 15 and 16 are example constructions of a phosphor encapsulated LEDdie.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Generally, previous optical fiber lighting designs suffered from highcoupling losses and were therefore very inefficient. An illuminationsystem in accordance with the present invention provides forsubstantially higher light coupling efficiency. Furthermore, theillumination system of the present invention offers an incoherent lightoutput that can appear to the human observer as arising from a singlepoint of light. In addition, exemplary embodiments of the presentinvention show that an array of LED dies can be utilized to provide ahigh density, remote source of light that can be output at one or morelocations. Moreover, exemplary embodiments of the present inventionprovide an array of LED dies that can be utilized to provide a highdensity, remote source of light that can produce one color, or multiplecolors, either individually, or simultaneously, at one or morelocations. In addition, the colors or color combinations of the sourcemay be made changeable to suit particular requirements of applicationsas conditions of use vary during operation. Other exemplary embodimentsare discussed below.

FIG. 1 illustrates an exemplary first embodiment of a remote lightingsystem 100 in accordance with an embodiment of the present invention. Anarray 102 of bright LED dies 104 are positioned in optical alignmentwith an array of optical elements 110, which can include a plurality ofpassive optical elements, such as focusing lenses 112 or opticalconcentrating elements, such as reflectors 120 (see FIG. 2). The arrayof optical elements 110 are in turn optically aligned to an array ofwaveguides 124, which can include a plurality of optical waveguides,such as optical fibers 122. The array of waveguides 124 can beconnectorized, where the connectorization can include a connector 132 tosupport and/or house the light-receiving ends of fibers 122. Theconnectorization can also include a connector 130 to support and/orhouse the output ends of fibers 122. Exemplary connector structures areshown in FIGS. 8–11, described below. As would be apparent to one ofordinary skill in the art given the present description, the output endsof the fibers 122 may be bundled to form a point-like source or ashaped-array, such as a linear array, circular array, or othershaped-array.

The array 102 is made out of an array of discrete LEDs 104, such as anarray of single LED dies or chips, which are mounted individually andhave independent electrical connections for operational control (ratherthan an LED array where all the LEDs are connected to each other bytheir common semiconductor substrate). LED dies can produce asymmetrical radiation pattern, making them desirable light sources forthe present invention. LED dies are efficient at converting electricalenergy to light and are not as temperature sensitive as most laserdiodes. Therefore, LED dies may operate adequately with only a modestheat sink compared to many types of laser diodes. In an exemplaryembodiment, each LED die is spaced apart from its nearest neighbor(s) byat least a distance greater than an LED die width.

In addition, LED dies can be operated at a temperature from −40° to 125°C. and can have operating lifetimes in the range of 100,000 hours, ascompared to most laser diode lifetimes around 10,000 hours or halogenautomobile headlamp lifetimes of 500–1000 hours. In an exemplaryembodiment, the LED dies can each have an output intensity of about 50Lumens or more. Discrete high-power LED dies are commercially availablefrom companies such as Cree and Osram. In one exemplary embodiment, anarray of LED dies (manufactured by Cree), each having an emitting areaof about 300 μm×300 μm, can be used to provide a concentrated (smallarea, high power) light source. Other light emitting surface shapes suchas rectangular or other polygonal shapes can also be utilized. Inaddition, in alternative embodiments, the emission layer of the LED diesutilized can be located on the top or bottom surface.

In an alternative embodiment, the LED array may be replaced with a whiteVCSEL array. The passive optical element array 110 may be used toredirect that light emitted from each VCSEL into a corresponding fiber122.

An aspect of the illustrated embodiment of FIG. 1 is the one-to-onecorrespondence between each light source, a corresponding passiveoptical element (lens, focusing, concentrating, or reflective element),and a corresponding waveguide. When powered, each LED die 104 acts as anindividual light source that launches light into a correspondingflexible individual fiber 122. The present exemplary embodiment includeslarge-core (for example, 400 μm to 1000 μm) polymer clad silica fibers(such as those marketed under the trade designation TECS™, availablefrom 3M Company, St. Paul, Minn.). Other types of optical fibers, suchas conventional or specialized glass fibers may also be utilized inaccordance with the embodiments of the present invention, depending onsuch parameters as, e.g., the output wavelength(s) of the LED diesources.

In addition, as would be apparent to one of ordinary skill given thepresent description, other waveguide types, such as planar waveguides,polymer waveguides, or the like, may also be utilized in accordance withthe present teachings.

Optical fibers 122 may further include fiber lenses on each of theoutput ends of the optical fibers. Similarly, the light receiving endsof the optical fibers may each further comprise a fiber lens. Fiber lensmanufacture and implementation is described in commonly owned andco-pending U.S. patent application Nos. 10/317,734 and 10/670,630,incorporated by reference herein.

One particular embodiment of the present invention, illustrated in FIG.13, described in further detail below, is the implementation of an LEDdriven automotive headlamp using flexible TECS™ fiber to interconnectthe light source and the headlamps. An aspect of this embodiment is theefficient coupling of the LED light into the TECS™ fiber in a way thatproduces the required luminance and beam pattern with a reduced numberof LED sources.

As illustrated in FIG. 2, a shaped reflector 120 may be added to eachLED die 104 to redirect light from the LED die 104 into a correspondingfiber 122, which can have an exemplary core diameter of about 600 μm to650 μm. In an exemplary embodiment, the structure of each reflectorprovides non-imaging light collection and distribution of theillumination to the light receiving fibers. The shaped reflectors 120may be made of a multilayer optical film (MOF), such as EnhancedSpecular Reflector (ESR) film available from 3M Company, St. Paul, Minn.Examples of MOFs are generally described in detail in U.S. Pat. Nos.5,882,774 and 5,808,794, incorporated by reference herein in theirentirety.

Alternatively, reflectors 120 may be formed in the appropriate shape ina metallic or plastic substrate or sheeting and coated with a reflectivematerial, such as silver, aluminum, or reflective multilayer stacks ofinorganic thin films. For example, an injection molded plastic film orsheeting may be formed. The reflector cavities formed therein may becoated with a suitable reflecting material. As described herein, thearray of reflectors can be oriented beneath, around, or above the LEDdies. In addition, the reflector cavity may be filled with an indexmatching material.

Referring back to FIG. 1, the individual fibers 122 are collectedtogether to provide remote lighting at a distance from the originallight sources. In a particular embodiment, the fibers 122 are broughttogether into a tight bundle in an output connector 130 that wouldreplace, e.g., the bulb or bulb filament in a spotlight or headlightassembly. A further description of an LED-based lighting assembly thatis implanted as a bulb replacement is described in a commonly pendingand co-owned application entitled “Solid State Light Device” Ser. No.10/726,225, incorporated by reference above.

Referring back to FIG. 2, in an exemplary embodiment, a bare blue or UVLED die can be utilized. In some exemplary embodiments, the LED die canbe coated, preferably on a light-emitting surface, with a phosphor layer106, such as YAG:Ce phosphor. The phosphor layer 106 can be used toconvert the blue output of the LED die into “white” light.

In an alternative embodiment, a collection of red, blue, and green LEDdies can be selectively placed in an array. The resulting emission iscollected by the array of fibers 122 so that the light emitted from theoutput ends of the fibers is seen by an observer as colored light or“white” light, when blended together in concert.

As shown in FIG. 2, the phosphor layer can be mounted or formed on anemitting surface of an LED die. In an exemplary embodiment of thepresent invention, as shown in FIG. 15, the phosphor layer 506 can beprecisely defined in order to substantially preserve, or reduce thedegradation of the étendue of the LED die surface emission. By“substantially preserve” it is meant that the étendue of the LED die ismaintained or is increased by a factor of two or less.

As shown in FIG. 15, a phosphor layer 506 is formed on LED die 504,which is surface mounted on substrate 540. In one example, the LED die504 is a blue or UV surface emitting LED. The substrate 540 provides aconductive surface for the LED die cathode and anode access. Forexample, one or more wirebonds 545 can be coupled from an electricalcontact surface 541 of the substrate to one or more bond pads 546disposed on the top surface of LED die 504. Alternatively, a wirebond545 may not be required to be bonded to the top surface of the LED die.

The phosphor layer 506 is disposed on or near an area of the LED diesubstantially corresponding to its emission surface. It is understoodthat LED dies typically emit radiation through more than one surface.Layer 506 can be formed to a substantially uniform thickness (forexample, about 75 μm to about 150 μm) and cured (partially or fully). Inthis exemplary embodiment, the layer 506 can then be converted into ashape or shapes by ablation, die cutting or other suitable techniqueswith minimal surface deformation to match the shape of the LED dieemission surface. Alternatively, undersizing or oversizing layer 506, orforming a shape different from the shape of the LED die emissionsurface, may be utilized. When utilizing an array of LED dies, thephosphor layer may be formed directly on the surface of each LED die or,alternatively, the phosphor layer can be part of a separate, coated filmof selectively patterned phosphor that is applied at or near thesurfaces of an array of LED dies. Additional phosphor orientation isdiscussed further below and in a commonly pending and co-ownedapplication entitled “Multiple LED Source and Method for AssemblingSame” Ser. No. 10/726,248, incorporated by reference above.

In an exemplary embodiment, phosphor layer 506 is formed as aphosphor-loaded encapsulant. For example, a YAG:Ce phosphor and a UVcure epoxy (such as a Norland NOA81 UV cure epoxy) can be utilized. Thephosphor-loaded encapsulant can be partially or fully cured. In apartially cured state, the phosphor encapsulant will flow around thewirebond, encapsulating the wirebond and adhering both the phosphor andthe wirebond to the surface of the die. If a hydrophobic encapsulantmaterial is used, the reliability of the electrical interconnect can beimproved. The phosphor encapsulant can be a low modulus material tominimize adverse effects due to the rising/falling temperature of theLED die. Here, the coefficient of thermal expansion (CTE) mismatchbetween the LED die material and the phosphor material can becompensated by such a deformable encapsulant.

If the phosphor encapsulant is fully cured, an additional adhesive layer(having about the same thickness as the wirebond) can be disposed on thesurface of the LED die. For example, the additional adhesive layer canbe formed on the LED die surface by deposition or dip-coatingtechniques. Thus, the additional adhesive layer can be utilized toencapsulate the wirebond and the phosphor encapsulant can be placed invoid-free contact (via the adhesive) with the surface of the LED die.

The above well-defined phosphor layer construction can be used tosubstantially preserve the étendue of the light emitting surface of theLED die. In this example, the area of the phosphor layer is formed to beabout the same as the area of the light-emitting surface. In addition,the thickness of the phosphor layer can be controlled to a suitableamount because as the phosphor layer has an increased thickness, theamount of light emitted from the sides of the phosphor layer willincrease. In addition, color temperature and color uniformity parameterscan be used to determine proper phosphor layer thickness for particularapplications.

In an alternative embodiment, shown in FIG. 16, the shape of thephosphor layer can be further defined to substantially preserve theétendue of the LED die source. Here, LED die 504 is coupled to substrate540, including contact surface 541, via wirebond 545. A phosphor layer506 is formed on the light-emitting surface of LED die 504 as isdescribed above. In addition, further ablation or dicing techniques maybe used to form angled surfaces 507 on the phosphor layer 506.

Referring back to FIG. 2, a reflector 120 can be used to couple lightemitted from the LED die 104 into fiber 122. Also, as shown in FIG. 2,the reflector can be formed so that it can slide over the LED die, sothat its lower opening 123 provides a close fit around the perimeter ofthe LED die 104. Alternative reflector designs include the additionaluse of a reflective coating on the substrate on which the LED die issupported. Other reflector designs are described in detail in thecommonly owned and co-pending patent application entitled “ReflectiveLight Coupler” Ser. No. 10/726,244, filed concurrently, and incorporatedby reference above.

An important aspect of this optical system is the shape of thereflective surface 121 of reflector 120. The reflector 120 can be formedby injection molding, transfer molding, microreplication, stamping,punching or thermoforming. The substrate in which the reflector 120 canbe formed (singularly or as part of an array of reflectors) can includea variety of materials such as metal, thermoplastic material, or MOF.The substrate material used to form the reflector 120 can be coated witha reflective coating or simply polished in order to increase itsreflectivity.

The shape of the reflector surface 121 is designed to convert theisotropic emission from the LED die, including a phosphor-coated LEDdie, into a beam that will meet the acceptance angle criteria of thelight receiving fiber, e.g., a TECS™ fiber, thus preserving the powerdensity of the light emitted from the LED dies. Once the light emittedby the LED die is collected and redirected by the reflector into thelight receiving fiber, the fiber(s) can be used to transport the lightto a distant location with low optical loss by total internalreflection. However, the light receiving fibers do not only serve totransport light. In addition, in accordance with embodiments of thepresent invention, by translating the fibers from the wider spacing ofthe LED die array to a tighter spacing or spacings, such as a tightpacked fiber bundle, light from the widely dispersed LED array can beeffectively concentrated into a very small area. Also, the opticaldesign of the exemplary TECS™ fiber core and cladding provide forshaping the light beams emerging from the bundled ends, due to theNumerical Aperture (NA) of the fibers at the input end as well as theoutput end. As described herein, the light receiving fibers performlight concentrating and beam shaping, as well as light transportation.

The étendue, ε, may be calculated using the formulaε=A*Ω≅π*A*sin² θ=π*A*NA ²where

-   Ω is the solid angle of emission or acceptance (in steradians);-   A is the area of the receiver or emitter,-   θ is the emission or acceptance angle, and-   NA is the Numerical Aperture.

For example, assuming an NA of 0.48 and a 600 micrometer (μm) diameterfiber core, the étendue that can be received and transmitted by thefiber is about 0.2 mm² steradians (sr). It is also assumed that amaximum emission surface of an exemplary LED die is about 300 μm×300 μm(or 90000 μm²) and that, in example implementations with the phosphor,the LED die has a nearly isotropic or Lambertian intensity distribution.Assuming a half-angle of 80 degrees, the étendue of the LED die is about0.28 mm² sr. Thus, while not all the light from the LED die may becollected by the fiber, a very large percentage of light (50% orgreater) can be collected and transmitted by the light receiving fiberutilizing the reflector surface design and orientation described herein.

As mentioned above, in an exemplary embodiment where a phosphor layer isused to convert the light output to “white” light, the phosphor layersize and/or thickness can be limited in order to preserve the étendue ofthe emitting surface of the LED die.

Improving or optimizing the reflector shape can increase or evenmaximize the light transfer into the fiber. The general geometry foroptimizing the reflector shape for a distributed light source withnearly Lambertian emission is shown in FIG. 3, which is a detail of thereflector surface 121 from FIG. 2 with angle and coordinate axisnomenclature added.

The general geometry in FIG. 3 shows that for a given point on themirror surface the light from the LED die strikes the mirror surface atan arrival angle θ_(i). Further, this point on the mirror is located at(x,y) and at this point the mirror makes an angle of φ_(j) relative tothe vertical. The reflected beam from the mirror surface can then beshown to be at an angle ofθ_(i)−2*φ_(j)=entrance anglerelative to the vertical which will be the entrance angle into thefiber.

The lighting constraints as imposed by the fiber and the LED in thisexample are:

1. LED/phosphor source size: 300 micrometer diameter 2. LED/phosphoremission angles: +/−80° 3. TECS ™ fiber size: 600 micrometer corediameter 4. TECS ™ fiber acceptance angle: NA 0.48 = entrance angle +/−28.7°

Some assumptions may be made to simplify the analysis at some expense ofgenerality.

Limitations of the following analysis are:

-   -   The full source size is not considered, as it is rectangular,        not circular as in this model—the actual source size is a square        300 micrometers by 300 micrometers.    -   The high angle light emitted from the part of the LED die        nearest the reflector is neglected.

The analysis assumptions are:

-   -   Light is reflected into (or directly enters) the fiber at an        angle less than the acceptance angle of ±28.7°. Thus the        constraint on the reflected beam is that |θ_(i)−2φ_(j)|≦28.7°.    -   The light emission angle from the LED/phosphor is nearly        isotropic and so may vary from 0° to 80° half-angle from the        vertical. The 80° maximum angle is used to establish the (x,y)        coordinates of the first analysis point.    -   Emission angles less than 28.7° are presumed to directly enter        the fiber.    -   The configuration is rotationally symmetric (see Limitations        above).

For the analysis, the lowest point on the reflector curve is assumed tobe at an incident angle controlled by the maximum angle of emissionθ_(i)=90−80=10°. This assumption then defines, for a value of x, the yor location of the reflector with orientation φ_(j). For example, if thereflector is assumed to start 30 micrometers to the right of the LED 104in FIG. 2, the (x, y) location of the first point on the reflector iscalculated to be 330*tan(90−80) or 58 micrometers.

Once the y location of the reflector point is known, the minimum angleto the nearest point on the LED/phosphor can be calculated as

$\tan^{- 1}\left( \frac{y}{\left( {x - 300} \right)} \right)$assuming the x coordinate system starts at the furthest edge of the(assumed round, in this example) LED, 300 micrometers away. For thereflection point at y=58 micrometers, the minimum emission angle is27.3°.

With the minimum and maximum emission angles θ_(i) calculated, themaximum and minimum reflector angle φ_(j) can be calculated such thatthe reflected ray would enter the fiber using Equation 1 and the firstconstraint above. Continuing the example, the reflector angle can bebetween about 0.7° and about 25.7°.

The reflector shape then may be numerically estimated by repeating thiscalculation for various angles less than the maximum of 80 degrees. InTable 1, the angle is decreased by one degree increments to theacceptance angle of the fiber, about 29°.

With the array of (x, y) values for the reflector, the incrementalreflector angle generated by this approach can then be estimated fromthe local derivative (difference) of the two (x, y) pairs nearest theselected (x, y) point. In the example for the maximum 80° angle, theinitial reflector angle is 17.5°.

From the plot, the polynomial regression fit for the curve generated bythis approach is y=5E−06x⁴−0.0068x³+3.6183x²−859.5x+76443 (R²=1.0)where, as shown in FIG. 3, the coordinate system origin is at the leftedge of the (assumed round) LED.

Table 1 below shows example calculations for a maximum emission angle of80 degrees and a separation of 30 micrometers from the edge of the LEDto the edge of the reflector. From Table 1, the calculated φ_(j) valuesfor the actual curve are calculated in the last column of the tablebelow. These values are coded in bold if the actual reflector willreflect the LED light into the fiber and in italics if some of the LEDlight will be reflected outside the acceptance angle of the fiber. Thecalculations show that with the exception of the top of the mirrorsurface, the emitted light can be reflected into the fiber. FIG. 4 is aplot of the curve shape of reflector points as outlined in the textassuming an 80 degree maximum emission angle and a 30 micrometerseparation between the LED and the reflector. This figure shows threerepresentations based the circular die model. The center Y plotrepresents the minimum inscribed circle from the center of the LED dieto a nearest edge, the diagonal Y represents the maximum circumscribedcircle from the center of the die to a corner, and the polynomial(center Y) is a polynomial fit of the center Y data. Note that while a4^(th) order polynomial is an exact fit, a 2^(nd) order polynomial has aR²=0.997.

At least one method to make the upper portion of the mirror surface alsoreflect light into the fiber would be to make the curve piecewisediscontinuous, for example, making the upper 400 micrometers portionsimply vertical (φ_(j)=0).

TABLE 1 Max angle x y min angle Φ min Φ max Φ_(j) 80 330 58.2 27.3 −0.725.7 17.5 79 332 64.5 26.4 −1.2 25.2 17.2 78 334 71.0 25.6 −1.5 24.716.9 77 336 77.6 24.9 −1.9 24.2 16.6 76 338 84.3 24.3 −2.2 23.7 16.3 75340 91.1 23.7 −2.5 23.2 16.0 74 342 98.1 23.2 −2.8 22.7 15.7 73 344105.2 22.7 −3.0 22.2 15.4 72 346 112.4 22.3 −3.2 21.7 15.1 71 348 119.821.8 −3.4 21.2 14.8 70 350 127.4 21.4 −3.6 20.7 14.5 69 352 135.1 21.0−3.8 20.2 14.2 68 354 143.0 20.7 −4.0 19.7 13.9 67 356 151.1 20.3 −4.219.2 13.6 66 358 159.4 20.0 −4.3 18.7 13.3 65 360 167.9 19.7 −4.5 18.213.0 64 362 176.6 19.3 −4.7 17.7 12.7 63 364 185.5 19.0 −4.8 17.2 12.362 366 194.6 18.7 −5.0 16.7 12.0 61 368 204.0 18.4 −5.1 16.2 11.7 60 370213.6 18.1 −5.3 15.7 11.4 59 372 223.5 17.9 −5.4 15.2 11.1 58 374 233.717.6 −5.6 14.7 10.8 57 376 244.2 17.3 −5.7 14.2 10.5 56 378 255.0 17.0−5.8 13.7 10.2 55 380 266.1 16.7 −6.0 13.2 9.9 54 382 277.5 16.5 −6.112.7 9.6 53 384 289.4 16.2 −6.2 12.2 9.3 52 386 301.6 15.9 −6.4 11.7 9.051 388 314.2 15.6 −6.5 11.2 8.7 50 390 327.2 15.4 −6.7 10.7 8.4 49 392340.8 15.1 −6.8 10.2 8.1 48 394 354.8 14.8 −6.9 9.7 7.8 47 396 369.314.6 −7.1 9.2 7.6 46 398 384.3 14.3 −7.2 8.7 7.3 45 400 400.0 14.0 −7.38.2 7.0 44 402 416.3 13.8 −7.5 7.7 6.7 43 404 433.2 13.5 −7.6 7.2 6.5 42406 450.9 13.2 −7.7 6.7 6.2 41 408 469.4 13.0 −7.9 6.2 5.9 40 410 488.612.7 −8.0 5.7 5.7 39 412 508.8 12.4 −8.1 5.2 5.4 38 414 529.9 12.1 −8.34.7 5.2 37 416 552.1 11.9 −8.4 4.2 4.9 36 418 575.3 11.6 −8.5 3.7 4.7 35420 599.8 11.3 −8.7 3.2 4.4 34 422 625.6 11.0 −8.8 2.7 4.2 33 424 652.910.8 −9.0 2.2 4.0 32 426 681.7 10.5 −9.1 1.7 3.7 31 428 712.3 10.2 −9.21.2 3.5 30 430 744.8 9.9 −9.4 0.7 3.3 29 432 779.3 9.6 −9.5 0.2 3.1 28434 816.2 9.3 −9.7 −0.3

The above reflector designs can be implemented in an array pattern in anumber of different implementations. For example, FIG. 7 shows anexample array of LED die sources 104, coupled to electrical interconnectmeans 142, which can be disposed on a circuit layer 141 (such asflexible circuits or semi-additive flexible circuits, including 3M™Flexible (or Flex) Circuits, available from 3M Company), which can bedisposed on a substrate. The LED dies 104 can be surface mounted tolayer 141 or, in one alternative, recessed into receiving aperturesformed in the flexible circuit layer. As an alternative to thewirebonding connections discussed above, an alternative electricalinterconnection of the LED array is made possible when utilizingflexible circuitry. For example, cantilevered leads can be formed bychemical removal of the dielectric, e.g. polyimide. This process canleaves one (or two) lead(s) cantilevered for ultrasonic or wire bondingto the electrical contact on the LED die. Such cantilevered interconnectleads may be smaller than wirebond wires and are substantially flat.

As mentioned above, phosphor elements 106 can be utilized to convert theoutput wavelength of the light from the LED die emission spectrum to thedesired illumination spectrum. Also, a corresponding array of reflectors120 can be utilized, forming an array 110 of passive optical elements,which can be formed in a microreplicated reflector sheeting 111, toefficiently couple light from the LED dies to a matching array ofoptical fibers 122, such as those shown in FIG. 1. The reflectorsheeting may comprise a MOF (such as that available from 3M company),with open reflector cavities formed therein. Alternatively, sheet 111can comprise reflectors 120 made from an injection molded material withreflective coatings (e.g., silver, aluminum, gold, inorganic dielectricstacks, or the like) disposed or coated on the inner walls (such assurface 121 from FIG. 2). Alternatively, reflectors 120 can be formedusing an embossed or punched metal sheet of reflector shapes.

In addition, phosphor layer 106, such as those described previously, canbe selectively patterned by incorporating a pattern of phosphor materialonto the top or bottom of the array layer 110. While FIG. 7 shows asquare LED die array, a regular or irregular array of LED light sourceswith associated optical elements, electrical interconnect, phosphorelements and reflective shapes could be used depending on applicationrequirements. In addition, with this exemplary design, fiducial marks149 can be used to align the respective array layers. An examplemultilayer construction for a multiple LED die source is described belowwith reference to FIG. 14.

FIG. 5 shows an example mounting structure or substrate 140 for the LEDdie 104. Substrate 140 can provide a low resistance thermal path toconduct heat away from the LED die 104. In this exemplary embodiment,LED die 104 is disposed in a well 151, where the bare LED die 104 can beattached to the substrate 140 by a conventional attachment, such as byusing a solder or metal (e.g., Au-Sn) reflow die attachment. Thesubstrate 140 can also support a circuit layer. In this exemplaryembodiment, the substrate 140 can be coated with a reflective coating143. In addition, as shown in FIG. 5, a cantilevered lead 148 is bondedonto the LED die from the interconnect circuit layer.

In FIG. 5, the phosphor material 106 can be located in the bottom of thereflector, coated on a sheet laminated to the bottom of the reflector,selectively patterned on a sheet laminated to the bottom of thereflector or, in a preferred method, deposited on top of the LED die.

In an exemplary embodiment, an interconnect circuit layer, rigid orflexible, can be utilized to provide interconnection. As describedherein, flexible circuit materials are available from the 3M Company. Inthe example shown in FIG. 5, a dielectric (e.g., polyimide) portion 145of the flexible circuit layer can be disposed on reflective coating 143.In addition, a conductive portion 147 of the flexible circuit layer,such as a copper conductor and/or other metallization (e.g., Ni/Au) canbe disposed on polyimide portion 145 for interconnection.

Alternatively, the flexible circuit layer can be inverted, and the bareLED die can reside in a recessed portion of the polyimide surface,directly on the metal/circuit layer 147. In this alternativeimplementation, wells need not be formed in the substrate material 140.An electrically insulating material with good thermal conductivity maybe disposed between the conductive portion of the flexible circuit andsubstrate, depending on the die electrical attachment requirements.Example implementations of interconnect circuitry are described in aconcurrently pending and co-owned application entitled “IlluminationAssembly” Ser. No. 10/727,220, incorporated by reference above.

A potentially lower performance, but perhaps lower cost alternativeembodiment, can include a conventional FR4 epoxy based printed wiringboard structure for electrical interconnect. In yet another embodiment,a low cost circuit can be prepared by patterning conductive epoxy orconductive ink onto a suitable substrate as required to connect the LEDdie array.

As mentioned above, a one-to-one fiber to LED die correspondence canprovide for better illumination efficiency. As an illustration of thisprinciple, FIG. 6 a shows a single fiber 125, with a core 125 a and acladding 125 b. FIG. 6 b shows a bundle 127 of nineteen fibers 125. Forexample, the effective area of a beam of light that is needed toilluminate bundle 127 is about 0.0017 square inches (0.011 squarecentimeters), for fibers 125 having an outer diameter of 0.028 incheseach, with a core diameter of about 650 micrometers. The area of thenineteen light transmitting fiber cores 127 is about 0.0010 squareinches (0.0065 square centimeters). With an assumed uniformlydistributed light source, the amount of light coupled into a waveguideis proportional to the input area of the waveguide; therefore, theefficiency ratio of light coupling in this figure is 0.0010/0.0017, orabout 60%.

An advantage of the present invention is an efficient launch of lightinto individual fibers of a fiber bundle. If using a single source, forexample, efficiency can drop significantly due to uncontrolled lightlaunch angles and to light coupling into the fiber cladding and theinterstitial spaces between the fibers in the bundle. Thus, traditionalsystems, which do not mate an individual LED to a corresponding fiber,may lose 25 to 40% of the emitted light due to the dark spaces betweenthe fibers in the bundle. Such systems would then require tight bundlingof more fibers and would still yield a less concentrated light.

In contrast, in the present invention, the light receiving fibers canthen be brought down into a very tight output array based on thediameter of the fibers, which thus yields a very compact, concentratedemission of light.

Because the individual light receiving fibers of the present inventionare relatively small in diameter they may be routed and bent as abundle, and the bundle may have a cross section of various geometricshapes, such as circular, helical, rectangular, or other polygonalshapes. Exemplary embodiments of the present invention allow a remotelypowered source to be concentrated and redirected to places wherelighting power is not normally obtainable in an efficient manner.

For example, in the application of vehicle headlights, such as thatillustrated in FIG. 13, the invention provides a highly concentratedlight source that is similar in size and shape to a lamp filament, sothe emitted light can be shaped and projected by a reflective surface orrefractive element. FIG. 13 shows an embodiment of a remote lightingsystem 300 for a motor vehicle that includes a coupler 301 to couple thevehicular power source (not shown) to an array of LED dies 304. The LEDdies 304 can be surface mounted on an interconnect circuit layer 341that can be disposed on a substrate 340, made from a thermallyconductive material, such as described above. In this embodiment, anarray of reflector shapes 320 can be disposed, such as by bonding, onthe interconnect circuit layer so that each bare die is surrounded onits perimeter by a reflective surface. Light emitted from the LED diesand collected/concentrated by the array of reflectors can optionally bedirected towards an array of lenses 312, which can focus the emittedlight into the input ends of corresponding fibers 322.

As shown in FIG. 13, an input connector 332 can be utilized to hold theinput ends of fibers 322. In this exemplary embodiment, the individualfibers can be bundled into two sets of fibers 351 and 352, so that thelight can be output at different locations (e.g., left and right vehicleheadlights 374 and 375). Output connectors 331A and 331B can be utilizedto hold the bundled sets of fibers in their respective headlights. Inthis manner, a “cool” headlight can be utilized, as the heat source(i.e., the light generating source—LED die array) is remote from theeventual illumination output area. This arrangement can reduce heatdamage to optical elements located in the headlight, such as reflectors,coatings, lenses, and other associated optics.

In another exemplary embodiment, the illumination system, such as system300 shown in FIG. 13, can further include an infrared sensor. In thisalternative embodiment, one or more of the array of LED dies cancomprise an infrared emitting LED die. Such infrared LED dies can beconventional IR LED dies, such as those available from Honeywell. Thesystem can further include a conventional IR detector to receive an IRsignal. This alternative embodiment can be utilized for collisiondetection applications. In addition, other types of sensors, forexample, ambient light sensors, can be employed for automatic dimmingapplications and/or for turning lights on automatically at dusk. Thus,in this alternative embodiment, the illumination system of the presentinvention can provide both illumination and telemetry. Alternatively, aninfrared transceiver device can be included, constructed as an integralpart of, or separate from, the illumination system.

FIGS. 8–11 illustrate various exemplary connector embodiments that canprovide low cost construction and that can be utilized in theillumination systems and assemblies described herein.

FIG. 8 illustrates a design for an input connector 132 a thatfacilitates top or bottom loading of fibers 122 and allows for an n×narray of fibers at a determined pitch that would correspond with thearray of light sources on the input end of the fiber cable assembly. Inthis exemplary embodiment, the connector 132 a is formed from a twopiece construction, with a top portion 133 having teeth 135 designed toengage fibers 122 in bottom piece 134. The bottom connector portion 134can include grooves 136 that receive fibers 122 and teeth 135 to providea secure fit. This structure not only allows for low cost assembly, butalso enables one to assemble a two-dimensional array in one step. Othertwo-dimensional connector designs can require “stacking” of layers ofV-groove connectors.

FIG. 9 illustrates an n×n array input connector 132 b where fibers 122could be installed from the top and the bottom. The connector 132 b ofthis exemplary embodiment is formed from a three piece construction,where the connector includes a center portion 131 having fiber receivinggrooves 138 that are enclosed by top portion 133′ and bottom portion134′. Alternatively, the connector 132 b can be formed from a singleintegrated construction. This design also allows making thetwo-dimensional connector in one step. To accomplish this, the assemblymachine in FIG. 12, for example, would have two fiber arrays instead ofone wide, linear fiber array.

FIG. 10 illustrates a design for an input connector 132 c with top orbottom loading, where spacers 139 are used to set the column pitchbetween fibers. This design also eliminates the need to stack v-groovelayers, by inserting “spacers” to create the two-dimensional array.

FIG. 11 illustrates a design for the output connector 130 for the fibercable assembly. This design can be for top loading and can accommodatedense packing of the fibers 122 for providing a concentratedillumination source. Other connector designs can also be utilized aswould be apparent to one of ordinary skill in the art given the presentdescription.

FIG. 12 illustrates an automated assembly procedure that may be used tobuild these devices. This figure depicts a process for Inline CableAssembly (INCA) that provides the capability to simultaneouslymanufacture and terminate cable assemblies. The INCA process isdescribed, for example, in co-owned U.S. Pat. Nos. 5,574,817 and5,611,017, the disclosures of which are hereby incorporated byreference. The INCA system 200 consists of an array of N fiber spools202, with fibers feeding the INCA assembly machine 210. The fibers 222are brought into an array with a particular, desired pitch using aprecision spaced guide comb 212. Typically this pitch will be the pitchrequired to terminate a particular connector design. Once on pitch, thefibers are routed to a connector assembly station 230, where connectorcomponents, consisting of at least a connector bottom 231 and aconnector cover 232, are moved into position above and below the fiberarray. At predetermined intervals along the length of the fiber array,the connector bottom 231 and cover 232 will be brought together tofurther align and then capture the fibers of the array. The connectorassembly can be mechanically or adhesively bonded to the fibers tocreate a terminated cable assembly, such as through the use oflaminating rollers 240 and adhesive tape 242. If a single connector isassembled, the output of the machine will be connectorized pigtails(cable with a connector on one end). By installing two connectors inopposing positions, spaced slightly apart, connectorized jumper cables250 (cable with connectors on both ends) will be output from themachine. From the point of connectorization, the assembled connector andfibers continue through the machine and a protective cable jacket isinstalled over the fiber array and connectors.

FIG. 14 shows an exploded view of an example construction of amultilayer, high-density solid state light source 400, that can becoupled to optical fibers to provide remote sourcing, consistent withthe embodiments described above. A first layer, or substrate 440, isselected to provide a base for supporting an array of LED dies 404. Asdescribed above, substrate 440 can comprise a material with high thermalconductivity, such as copper, or the like. In addition, substrate 440can be electrically conductive, and can provide a power or ground busfor the array of LED dies 404. The LED dies 404 can be bonded tosubstrate 440 using conventional techniques, including solder,adhesives, or the like. An adhesive layer 405 can then placed over theLED dies. The adhesive layer 405 can include a pattern of cut-outscorresponding to the position and pitch of the LED dies.

To provide electrical connections, a patterned flexible circuit layer441 can then be placed over the patterned adhesive layer 405. Theflexible circuit layer 441 includes an electrical conductor pattern 442to provide contact to the LED dies 404. Typically, LED dies require twoelectrical connections—in some designs, one connection is on top of theLED die and one is on the bottom of the LED die and in other designs,both connections are on top. In this exemplary embodiment, flexiblecircuit layer 441 includes cut-outs corresponding to the array of LEDdies. Top connections to the LED dies are made via the circuit patterns442 on the flexible circuit layer 441 and bottom connections can be madethrough the substrate 440. Fiducial marks 449 can be utilized to ensureproper alignment between the substrate and flexible circuit layer 441.

An array of passive optical elements 410, such as reflectors 420 formedin a microreplicated reflector sheet 411 can be used to provide couplingof the light emitted from the LED dies to the corresponding array ofoptical waveguides. In this exemplary embodiment, sheet 411 includes anarray of reflectors 420. The reflectors 420, consistent with theembodiments described above, can be formed in a multilayer optical filmor, alternatively, they can comprise molded, machined, or embossedshapes formed from a reflective (e.g., plastic, metallic) sheet that ispatterned at the same pitch as the LED dies. In addition, the reflectorscan also include a lens shape within the reflector cavity. Further,patterned phosphors can be included in the reflector cavities, or bondedto the top or bottom of the sheet 411.

An additional patterned adhesive layer 445 can be used to attach array410 to the flexible circuit layer 441. Again, fiducials 449 can beutilized for alignment. The adhesive material can be selected to providehigh bond strength and/or insulation between the substrate and the arrayof reflectors. Further, the adhesive material can mitigate stresses dueto any mismatch between the coefficient of thermal expansion (CTE) ofthe substrate and the reflector sheeting.

In an alternative embodiment, the position of the flexible circuit layerand the reflector array can be interchanged. For example, the flexiblecircuit layer leads can be routed through the reflector cavity to attachto the LED die bonding pads.

The illumination assemblies and systems described above have severaladvantages over prior systems. First, smaller LED dies, such as thosedescribed above, with lower heat outputs can be utilized withoutsuffering loss in illumination intensity. In the examples discussedabove, the LED dies in the array are physically separated to avoidthermal hot spots in the mounting structure. This structure allows theLED dies to be electrically driven harder, with more output illumination(and hence, a brighter output beam emitted from the output ends of thefibers). Tightly packing large numbers of LED die is a long termreliability concern since local heating, even with a globally efficientthermal conduction mechanism, can cause reduced LED lifetime and inextreme cases catastrophic failures. Spacing the LED dies farther apartthan the width of the LED die allows reasonably thermally conductivesubstrates to extract the heat from the LED array without local hotspots. The LED dies may also be safely operated at higher currents andlight outputs than stated in the normal operating specifications, ifsufficient heat extraction is provided. Moreover, as compared tofilament light sources, the LED die array of the present invention doesnot generate intense heating in the forward directed beam, which can bea result of filament heating. This intense heat can cause damage topolymer lenses and reflector assemblies that are sometimes employed inlighting elements, such as automobile headlights.

A second advantage is the one fiber per LED coupling. Prior systemscoupled dense arrays of LEDs into a large diameter fiber or fiberbundle. Dense LED arrays have the previously mentioned reliabilityproblems, but their implementation has been justified as providing thebest efficiency for coupling light into the fiber (at the expense ofreliability). Providing one fiber per LED source allows the LED dies tobe physically separated, minimizing localized thermal effects from denseconcentrations of LEDs as discussed above.

Another advantage is the electrical interconnect wiring. A thin (forexample, 25 to 50 micrometer) layer of electrical wiring as exemplifiedby flexible circuitry, such as the flexible circuitry describedpreviously, provides electrical interconnect, some thermal conduction ofheat from the die, and a flat electrical interconnect structure whichmay be laminated. The resulting construction overall is a very thinlayer, so that the optical performance of this layer is not critical.The thin, flat layer allows the entire array to be laminated into ahighly reliable solid or nearly solid block of material with the LEDarray (on a substrate) bonded to the electrical interconnect layer,which can in turn be bonded to the reflector sheeting. The advantages ofparticular implementations of interconnect circuitry are described inthe pending and co-owned application entitled “Illumination Assembly”Ser. No. 10/727,220, incorporated by reference above.

An additional advantage of the illumination devices described herein isthe lamination or encapsulation of the entire assembly. Since the LEDarray and the reflector cavities may be filled with a solid material,for example an epoxy or molded polycarbonate, the entire assembly may belaminated into a block with no voids. Voids in electrical equipment canbe reliability issues in some applications because water tends tocollect in polymer voids, leading to long-term reliability issues.

Also, a beam-forming reflector can be disposed in front of the LED die.Further, the reflector structure may be made from MOF, which can bedrawn into the reflector shape while retaining reflectivity over thevisible light wavelengths and over a wide range of incident angles.

Another advantage is the described phosphor placement that provides fora selected output color. Prior attempts utilize phosphor in the cavityholding the LED. This bulk phosphor deposition requires significantamounts of relatively expensive phosphor and, since the phosphor emitslight isotropically, this inherently degrades the étendue of the LEDsource by making the LED appear larger than its actual size. This, inturn, can significantly reduce the coupling efficiency of the light intoa fiber or other waveguide, as described in the embodiments above.

The phosphor 106, such as shown in FIG. 5, may be coated on a sheet andlaminated into the structure at the bottom (or top) of the reflector, orbe directly deposited on the surface of the LED. Using a coated layer ofphosphor results in a very uniform, thin layer of phosphor in a binderthat efficiently converts the LED energy into “white” light. Thephosphor layer can be precisely defined so not to appreciably increasethe apparent size of the LED source, thereby preserving the étendue ofthe LED and improving the coupling efficiency of the system. Whendepositing the phosphor-loaded epoxy directly or indirectly onto theemitting surface of the LED, the amount of phosphor can be reduced andthe size of the LED emission area can be precisely maintained throughprecise volume deposition of very small volumes of phosphor.

Another advantage of the present invention is the ability to tailor thecolor spectrum emitted from the LED die array. While “white” light maybe made from a combination of LED die colors, several exemplaryembodiments utilize a phosphor layer to convert blue or UV radiationinto a broad spectrum, i.e., “white” light. Using different phosphorsacross the LED die array can produce “white” light with a desired colortemperature. Similarly, a variety of colors may be produced by tailoringthe phosphor used across the LED dies.

While placing the phosphor-coated sheet on top of the reflector arraymay not result in the most efficient coupling of light energy into afiber array (because of the limited acceptance angle of the opticalfiber), such a construction might be advantageous for a large surface,high divergence array, again without localized hot spots from denseconcentrations of LEDs.

While the present invention has been described with a reference toexemplary preferred embodiments, the invention may be embodied in otherspecific forms without departing from the scope of the invention. Forexample, while the present exemplary embodiments have been shown in thearea of automotive headlights, the present illumination system may beused in aircraft, marine, medical, industrial, home, and even otherautomotive applications. Accordingly, it should be understood that theembodiments described and illustrated herein are only exemplary andshould not be considered as limiting the scope of the present invention.Other variations and modifications may be made in accordance with thescope of the present invention.

1. An illumination device, comprising: a plurality of independentlycontrollable LED dies to generate optical radiation; an interconnectcircuit layer to provide electrical connection for the plurality of LEDdies, wherein the interconnect circuit layer is disposed on a thermallyconductive and electrically insulating substrate; a plurality of opticalwaveguides, wherein each of the plurality of optical waveguides includesa first end and a second end, wherein each first end is in opticalcommunication with a corresponding LED die of the plurality of LED dies;and an array of optical elements, wherein each optical element of thearray of optical elements is interposed between a corresponding firstend of the optical waveguide and the corresponding LED die.
 2. Theillumination device according to claim 1, wherein the plurality ofoptical waveguides comprises a plurality of optical fibers.
 3. Theillumination device according to claim 2, wherein the plurality ofoptical fibers comprises a plurality of polymer clad silica fibers, eachhaving a core diameter of about 400 to about 1000 micrometers.
 4. Theillumination device according to claim 2, wherein the second ends of theplurality of fibers are bundled to form a single light illuminationsource.
 5. The illumination device according to claim 2, wherein thesecond ends of the plurality of fibers are bundled into separate groupsto form separate light illumination sources.
 6. The illumination deviceaccording to claim 1, wherein the array of optical elements comprises anarray of passive optical elements.
 7. The illumination device accordingto claim 6, wherein the array of passive optical elements comprises anarray of optical concentrating elements.
 8. The illumination deviceaccording to claim 1, further comprising: a projecting element toreceive and project optical radiation emanating from the second ends ofthe plurality of optical waveguides.
 9. The illumination deviceaccording to claim 1, wherein the plurality of optical waveguidescomprise a plurality of optical fibers, further comprising: a pluralityof optical focusing elements to receive and focus optical radiationemanating from the second ends of the optical fibers.
 10. Theillumination device according to claim 9, wherein the optical focusingelements comprise fiber lenses, wherein each second end comprises acorresponding fiber lens.
 11. The illumination device according to claim1, wherein each of the first ends comprises a corresponding fiber lens.12. The illumination device according to claim 1, further comprising awaveguide connector to support each of the first ends of the pluralityof waveguides.
 13. The illumination device according to claim 1, whereinthe array of optical elements comprises an array of reflectors.
 14. Theillumination device according to claim 13, wherein the array ofreflectors comprises an array of reflectors formed in multilayer opticalfilm.
 15. The illumination device according to claim 13, wherein thearray of reflectors comprises an array of open-cavity metallizedreflectors.
 16. The illumination device according to claim 13, whereineach reflector receives at least a portion of the light emitted by acorresponding LED die at an incident angle of about 0.7 degrees to about25.7 degrees relative to the normal from the LED die top surface. 17.The illumination device according to claim 13, wherein the LED dies aredisposed proximate to a first surface of said array of reflectors suchthat light emanating at angles up to 80 degrees as defined relative to aline normal to an emission surface of the LED dies is reflected by thearray of reflectors.
 18. The illumination device according to claim 13,wherein the array of reflectors are disposed relative to the LED diesand the first ends of the optical waveguides to substantially preservean étendue of each of the plurality of LED dies.
 19. The illuminationdevice according to claim 1, wherein each LED die has a width andwherein each LED die is disposed on the interconnect circuit layer at adistance greater than its width from all neighboring LED dies.
 20. Theillumination device according to claim 1, wherein each LED die isoptically coupled into a different one of the plurality of waveguides.21. The illumination device according to claim 1, wherein each LED diehas a width and wherein each LED die is disposed on the interconnectcircuit layer at a distance greater than its width from all neighboringLED dies.
 22. The illumination device according to claim 1, wherein eachLED die is surface mounted on the interconnect circuit layer.
 23. Theillumination device according to claim 1, wherein the interconnectcircuit layer comprises a flexible material.
 24. The illumination deviceaccording to claim 1, wherein the interconnect circuit layer has athickness of from about 25 μm to about 50 μm.
 25. The illuminationdevice according to claim 1, wherein the interconnect circuit layerincludes a cantilevered lead adaptable for one of wire bonding andultrasonic bonding.
 26. The illumination device according to claim 1,wherein the plurality of optical elements comprises an array ofreflectors, and wherein the LED dies and the array of reflectors areencapsulated.
 27. The illumination device according to claim 1, whereina surface of at least one LED die is coated with a phosphor layer. 28.The illumination device according to claim 27, wherein the phosphorlayer is deposited directly onto an emission surface of the at least oneLED die in an amount sufficient to convert the output wavelength of theat least one LED die and to substantially maintain an étendue of the atleast one LED die.
 29. The illumination device according to claim 28,wherein the phosphor layer is precisely defined in size to match anemitting surface of the corresponding LED die.
 30. The illuminationdevice according to claim 29, wherein the phosphor layer furthercomprises tapered portions.
 31. The illumination device according toclaim 27, further comprising a wire bond coupling the LED die to theinterconnect layer, wherein the phosphor layer adheres the wirebond tothe LED die.
 32. The illumination device according to claim 1, whereinthe array of optical elements comprises an array of reflectors, andfurther comprising a phosphor layer coated on at least a portion of asheet, said sheet disposed on one of a top surface and a bottom surfaceof the array of reflectors.
 33. The illumination device according toclaim 32, wherein the phosphor layer sheet comprises a sheet ofselectively patterned phosphor regions, wherein each phosphor region ispositioned to cover an emission entrance region of each reflector. 34.The illumination device according to claim 1, wherein a phosphor layeris laminated on one of the top surface and the bottom surface of thearray of optical elements.
 35. The illumination device according toclaim 1, wherein each LED die is disposed in a recessed aperture of theinterconnect circuit layer.
 36. The illumination device according toclaim 1, wherein the array of optical elements comprises an array ofreflectors, wherein each reflector of said array has an entranceaperture and an exit aperture, and wherein an emission surface of eachLED die is spaced below said entrance aperture.
 37. A vehicularheadlight comprising the illumination device according to claim 1.